Potassium (40K) having a mass of 40 has a sufficiently long half-life in spite of a radioisotope, such that it is used for experiments of physics, biology, and geochronology. Many applications for 40K use radioactive decay characteristics, but atomic physicists are interested in this radioisotope because 40K is one of the two stable fermionic alkali atoms that may be currently laser-cooled. Once the atoms are laser-cooled, cryogenic atoms may be used for various experiments in quantum precision measurement and quantum information. As compared with cryogenic bosonic atoms, fermions follow the Fermi statistics that prevent fermions from being in the same quantum state. This attribute provides a basis for generating cryogenic atomic samples for observing suppressed collisional dynamics for use in development of a high-precision quantum sensor. By using the fermions with bosons in an atom-based quantum simulator, particularly in an experiment related to simulating a condensed matter physics in which trapped atoms correspond to electrons in solid, potential results of a wide range of experiments are improved.
Particularly, 40K is a relatively heavy alkali as compared with 6Li, and thus provides many advantages for laser cooling and trapping. 6Li has a natural abundance ratio high (7.5%) enough to implement a Zeeman slower, but a natural abundance ratio of 40K is very low (0.012%), such that it is very difficult to directly apply the Zeeman slower for a high flux atomic beam source. Unfortunately, most experiments using 40K require an isotopically enriched source for the purpose of the appropriate number of trapped atoms, typically up to about 5%.
In order to obtain such an enriched source for a laser cooling experiment, it is necessary to perform a time-consuming process of manufacturing a dispenser or to purchase a pre-manufactured source at high cost. Therefore, it is particularly important to adopt a new technology for improving an atom trapping efficiency in an experiment using 40K atoms.
In many experiments, a two-dimensional magnetic-optical trap (2D MOT) is a method selected in order to obtain an atomic beam flux source for laser cooling. The 2D MOT has significant advantages as compared with other atomic sources such as the Zeeman slower and a background vapor due to a background pressure maintained to be low, a slow velocity of an output atomic beam flux, and tens of milliseconds. These slow atoms are efficiently captured by a three-dimensional magnetic-optical trap (3D MOT) and are additionally cooled into a sub-Doppler domain, such that cryogenic atoms may be created. In addition, a general size of a system tends to become relatively small as compared with the Zeeman slower, and the system is likely to be smaller with development of a laser beam transfer technology. An atomic beam flux may control a 2D MOT laser beam to easily and effectively turn on and turn off the 2D MOT laser beam.
In a conventional 2D MOT in which a frequency is not modulated, there is a problem that an atomic beam flux is not increased even though a laser intensity is increased.